1. Field of the Invention
The invention relates to data communication systems, and more particularly to a wireless local area network (LAN) communication system in which mobile units associate with stationary access points having communications characteristics defined by the particular country in which the LAN is installed.
2. The Background Art
A wireless LAN may be implemented by remote mobile units that send messages to and receive messages from base stations or Stationary Access Points using wireless infrared or radio communication links. Each Stationary Access Point covers a limited area, so a typical network may have several Stationary Access Points.
One protocol that may be used is the IEEE 802.11 Standard that defines physical and data link layers for wireless local networks. The standard defines, among other things, the wireless LAN medium access control (MAC) and physical (PHY) layer specifications.
For a message to be transmitted, a mobile unit first becomes associated with a Stationary Access Point. Association refers to the process of synchronizing a mobile unit with a Stationary Access Point for communication, and is initiated by the mobile unit. The mobile unit first listens to the broadcasts over the airwaves and determines which Stationary Access Points are within range of the mobile unit, and then requests association with a particular Stationary Access Point according to certain criteria. At any point in time, a mobile unit is typically associated with only one Stationary Access Point. A single Stationary Access Point can be associated with multiple mobile units.
With the ever-growing global market, it is common for users to travel from country to country. A problem therefore occurs, in that one country may allocate a different portion of the frequency spectrum to wireless communications than another country. Additionally, different countries may have different regulations regarding power output of wireless communications. These allocations and regulations may prevent a mobile unit which is designed for use in one country from working (or being allowed to work) in another country.
What is needed, then, is a system and method for allowing a mobile unit to meet regulatory requirements and adapt to and communicate with Stationary Access Points having different communication characteristics.
The present invention relates to an apparatus and a method for automatically adapting a mobile unit to communication requirements of a particular country or geographic region. To achieve this capability, a method operates on a wireless data communications network including a mobile unit and one or more access points, wherein the method includes the steps of: receiving in the mobile unit announcement messages broadcast by one or more of the access points, each of said messages having a unique frequency characteristic associated with the geographic location of the access point from which it was sent; determining, in said mobile unit, an allowable frequency set in the geographic region associated with the access point from which each of said messages was sent; and adjusting the frequency set of the mobile unit to send messages on said allowable frequency set. The invention may then adjust other operating characteristics in a similar fashion.